They never held the Ukraine. Ukrainian Bolsheviks overthrew the government in Ukraine in 1922. They wanted to be apart of the USSR.
There is no chance in hell Russia holds Ukraine if the Ukrainian's mount an insurgency. The ability for everyday people to communicate today vs even 20 years ago makes it 1 million times easier to coordinate an insurgency.
The internet, social media, and technology are a game changer. Putin's got 3 options in my opinion.
Best option.
1. He can try to negotiate a full surrender of Donbask from Ukraine and pull his troops out of the rest of Ukraine. Maybe get a no NATO deal.
Bad option.
2. He can try to take out the government and put in his own loyalists. But the Army will not likely follow and the people will revolt. If Zalenskey is killed he will be a rallying cry for decades.
Worst Option
3. Try to occupy. You think the language is benefit for Putin, but it's actually a negative. Most soldiers, Russian soldiers included, follow orders because they think they are doing the right thing. As soon as you stop fighting and try to occupy, you develop relationships. Putin will lose the narrative with his own soldiers. They will quickly realize they didn't overthrow a dictator, but a comedian trying to do right by his people.
Not to mention, there are so many Ukrainian's. 20x the entire Taliban in military age veterans alone. They will set ambushes, use IED's, and of course we are going to feed them shitloads of hardware.
But the biggest issue is money. Russia was already too broke. After sanctions it will be impossible to financially support an occupation of that size for more than a few months. If that.